The efficiency of mechanical power development during muscular shortening and its relation to load

When shortening occurs during a maintained isotonic contraction, as Aubert (1956) found during shortening at constant speed, the ‘efficiency’ remains very constant throughout, even over a considerable range of length. The efficiency varies largely with the load P, being zero at P = 0 and P = P₀ (isometric). Near its maximum around P /P₀ = 0·5 the efficiency (in frog sartorii at 0 °C) is consistently about 0·45. The form of the relation between efficiency and load is discussed, particularly in view of recent findings on the heat of shortening of muscle. The mechanical power developed during shortening is greatest when P/P₀ = v/v₀ = about 0·3; but the efficiency here is only 3 to 5% less than its maximum.